This invention relates to a blood pressure measuring process and apparatus for automatically measuring systolic and diastolic blood pressures.
As is well known, typical conventional measurement of blood pressure is obtained by the use of an inflatable cuff which is wrapped around the arm of a patient or person. The cuff is inflated to occlude blood flow, then the pressure in the cuff is gradually decreased. At the instant a first acoustic pulse, called a Korotkov sound, is detected, the cuff pressure represents the systolic blood pressure. The pressure in the cuff is further decreased until the acoustic pulses disappear. At this point, another pressure reading is taken which serves as the diastolic blood pressure. However, it is often the case that the Korotkov sounds disappear even though the cuff pressure is higher than the true diastolic blood pressure, and they again appear when the pressure in the cuff is futher decreased, as shown in FIG. 1. The interval of disappearance of the Korotkov sounds, which is typical of some patients, is called the auscultatory gap. By the reason of the above, accurate measurments of diastolic blood pressure of some patients are not always obtained by detecting for the disappearance of Korotkov sounds.
A proposed measuring apparatus for accurately and automatically measuring diastolic blood pressure of patients having an auscultatory gap is shown in the published specification No. 35798/1974 of a Japanese patent application. This reference discloses a blood pressure measurement which is discontinued if Korotkov sounds are not detected within a predetermined time period of about 7 seconds, which corresponds to a pressure decrease of 20 mmHg after the Korotkov sounds disappear. Since the measurement shown in this reference always requires a time period of 7 seconds after the detection of the last Korotkov sounds, it is disliked by patients whether or not they have an auscultatory gap Further, inaccurate measurement is often unavoidable since the rate of pressure decrease often varies, causing a variation in the predetermined time period.